This application claims the benefit of Korean Patent Application No. 1999-46345, filed on Oct. 25, 1999, under 35 U.S.C. xc2xa7 119, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display (LCD) device and a method of manufacturing the same.
2. Description of Related Art
FIG. 1 is a cross sectional view illustrating a typical LCD device. As shown in FIG. 1, the LCD device includes lower and upper substrates 2 and 4 with a liquid crystal layer 10 interposed therebetween. The lower substrate 2 has a thin film transistor xe2x80x9cSxe2x80x9d (TFT) as a switching element and a pixel electrode 14, and the upper substrate 4 has a color filter 8 and a common electrode 12. The pixel electrode 14 is formed over a pixel region xe2x80x9cPxe2x80x9d serves to apply a voltage to the liquid crystal layer 10 along with the common electrode 12, and the color filter 8 serves to implement natural colors. A selant 6 seals an edge of the lower and upper substrate 2 and 4 to prevent a leakage of the liquid crystal.
FIG. 2 is a plan view illustrating the lower array substrate of the typical LCD device. As shown in FIG. 2, the lower array substrate 2 includes gate lines 22 arranged in a transverse direction and data lines 24 arranged in a longitudinal direction perpendicular to the gate lines 22. The TFTs xe2x80x9cSxe2x80x9d are arranged near a crossing point of the gate and data lines 22 and 24. The pixel electrodes 14 are arranged on a region defined by the gate and data lines 22 and 24. Each of the TFT xe2x80x9cSxe2x80x9d includes a gate electrode 26, a source electrode 28 and the drain electrode 30. The gate electrode 26 extends from the gate line 22, and the source electrode 28 extends from the data line 24. The drain electrode 30 is electrically connected with the pixel electrode 14 through a drain contact hole 30xe2x80x2. Data and gate pads 21 and 23 are arranged at terminal portions of the gate and data lines 22 and 24, respectively. Storage capacitors xe2x80x9cCstxe2x80x9d are formed over a portion of the gate line 22.
A process for manufacturing the LCD device described above is very complex. Especially, the lower array substrate is manufactured through several mask processes. The process of manufacturing the lower array substrate is explained below with reference with FIGS. 3A to 3E.
FIGS. 3A to 3E are cross sectional views taken long lines Axe2x80x94A and Bxe2x80x94B of FIG. 2, respectively. First, as shown in FIG. 3A, a metal layer is deposited on a substrate 1 using a sputtering technique after removing alien substances and organic materials and cleaning the substrate to enforce an adhesion between the substrate 1 and the metal layer. Thereafter, the metal layer is patterned into a gate line 22 including a gate electrode 26 using a first mask. The gate line 22 is made of a low resistive material such as aluminum or molybdenum to lower a RC delay. Pure aluminum is a bad corrosion resistance and may cause a line defect due to a hillock in a subsequent process. Therefore, an aluminum alloy or a two or three-layered aluminum is usually used. A portion of the gate line 22 serves as a first capacitor electrode.
As shown in FIG. 31B, a gate insulating layer 50 is deposited on the exposed surface of the substrate 1 while covering the gate line 22 and the gate electrode 26. The gate insulating layer 50 has a thickness of 3000 xc3x85 and is usually made of SiNx or SiOx. A pure amorphous silicon layer 52 and a doped amorphous silicon layer 54 are sequentially deposited on the gate insulating layer 50. Then, the amorphous silicon layer 52 and the doped amorphous silicon layer 54 are patterned into an active layer 55 and a semiconductor island 53. The doped amorphous silicon layer 54 is called an ohmic contact layer and serves to reduce a contact resistance between the active layer 55 and a metal layer that will be formed in later process.
Subsequently, as shown in FIG. 3C, a metal layer is deposited on the semiconductor layers 53 and 55 and is patterned into source and drain electrodes 28 and 30 using a third mask. The source and drain electrode 53 and 55 are usually made of chromium or chromium alloy. At the same time as the source and drain electrodes 28 and 30, the data lines 24 are formed. A second capacitor electrode 58 is formed on the gate insulating layer 50 and overlaps a portion of the gate line 22 in order to form a storage capacitor. In other words, using the third mask, the data line 24, the source and drain electrodes 28 and 30, and the second capacitor electrode 58 are formed. Using the source and drain electrodes 28 and 30 as a mask, a portion of the ohmic contact layer 54 over the gate electrode 26 is etched. If the portion of the ohmic contact layer 54 over the gate electrode 26 is not etched, it brings about bad electrical characteristics and a bad performance of the TFT xe2x80x9cSxe2x80x9d. Etching the portion of the ohmic contact layer 54 over the gate electrode 26 requires special attention. It is because the etching uniformity directly affects electrical characteristics of the TFT.
As shown in FIG. 3D, a passivation film 56 is formed over the substrate 1 using the fourth mask in order to protect the active layer 55. The passivation film 56 may affect electrical characteristics of the TFT due to an unstable energy state of the active layer 55 and alien substances generated during the etching process, and therefore it is usually made of an inorganic material such as SiNx and SiO2 or an organic material such as benzocyclobutene (BCB). The passivation film 56 also requires a high light transmittance, a high humidity resistance and a high durability. The passivation film 56 includes two contact hole: the drain contact hole 30xe2x80x2; and a capacitor contact hole 58xe2x80x2.
Therefore, as shown in FIG. 3E, a transparent conducting oxide layer is deposited on the passivation film 56 and is patterned into the pixel electrode 14 using a fifth mask. The pixel electrode 14 is usually made of indium tin oxide (ITO). The pixel electrode 14 is electrically connected with the drain electrode 30 through the drain contact hole 30xe2x80x2 and with the second capacitor electrode 58 through the capacitor contact hole 58xe2x80x2.
The process for manufacturing the conventional LCD device described above includes at least five masks. Further, when the gate electrode is made of aluminum, at least two masks are required to overcome an occurrence of the hillock that may be generated on the surface of the aluminum layer. Therefore, manufacturing the TFT array substrate basically requires five or six masks. Such a mask process includes various processes such as a cleaning, a depositing, a baking, an etching and the like. Therefore, even a reduction of one mask causes a short processing time, a low production cost and a high manufacturing yield.
For the foregoing reasons, there is a need for a liquid crystal display device manufactured by the mask process decreased in number.
To overcome the problems described above, preferred embodiments of the present invention provide a liquid crystal display device manufactured the mask process decreased in number and a method of manufacturing the same.
Preferred embodiments of the present invention further provide the liquid crystal display device having a short processing time and a high manufacturing yield.
In order to achieve the above object, the preferred embodiment of the present invention A method of manufacturing a liquid crystal display device, including: providing a substrate; depositing sequentially a first metal layer and a first insulating layer on the substrate; patterning the first metal layer and the first insulating layer using a first mask to form a gate line and a first gate insulating layer; depositing sequentially a second gate insulating layer, a pure semiconductor layer, a doped semiconductor layer and a second metal layer over the whole substrate; patterning the second metal layer using a second mask to form a data line, source and drain electrodes, a capacitor electrode, the capacitor electrode overlapping a portion of the gae line; etching the doped semiconductor layer between the source and drain electrodes to form a channel region; depositing a third insulating layer over the whole substrate; patterning the third insulating layer using a third mask to form a passivation film, the passivation film having a smaller width than the data line and covering the source and drain electrodes and exposing a portion of the drain electrode and the capacitor electrode; depositing a transparent conductive material layer over the whole substrate; and patterning the transparent conductive material layer using a fourth mask to pixel electrode, the pixel electrode contacting the drain electrode.
The gate line includes a gate pad formed at its terminal portion, the gate pad including at least one pad contact hole. The method further includes forming gate pad electrode using the fourth mask, the gate pad electrode contacting the gate pad through at least one pad contact hole. A crossing portion between the gate line and data line is insulated by the second insulating layer, the pure semiconductor layer and the doped semiconductor layer.
The preferred embodiment of the present invention further provides a liquid crystal display device, including: a substrate; a thin film transistor formed on the substrate, including: a gate line having a gate electrode; first and second insulating layers; an active layer; and source and drain electrodes; a pixel electrode overlapping a portion of the gate lines and contacting the drain electrode; and a storage capacitor including: a portion of the gate line as a first electrode; a second electrode overlapping the portion of the gate line; and the first and second insulating layers, the pure semiconductor layer and the doped semiconductor layer interposed between the gate line and the pixel electrode as a dielectric layer.
The LCD device according to the preferred embodiment of the present invention has the following advantages. First, since the LCD device can be manufactured using only four masks, the processing time becomes decreased and the manufacturing yield is high. Further, since the process is reduced in number, the production cost is low. Since the gate pads include a plurality of the pad contact holes, a contact resistance between the pixel electrode and the gate pad becomes lowered due to the side contact.